In a hazardous or toxic chemical environment, such as may be found during chemical warfare, or in other situations where toxic chemicals are used, personnel may be exposed to various organic chemical vapors. Shelters equipped with detoxified air supply systems have been developed for use in military or other settings. Personnel shelters for use again nuclear, biological or chemical warfare agents typically employ carbon filters, such as ASC Whetlerite filters, to sorb toxic agents from the air flowing into the shelter. Filter cartridges have a limited life and must be replaced when the filtration capacity has been expended. Replacement is expensive and forms a significant logistic burden.
Membrane systems that can separate organic vapors from air are known. For example, U.S. Pat. No. 4,553,983 describes a method of removing and recovering organic vapors from air, using a rubbery membrane. Rubbery membranes are typically 50 to 100 times more permeable to large organic molecules than to oxygen and nitrogen, so the organic agent will be concentrated in the permeate stream, leaving a residue stream containing oxygen and nitrogen. However, the oxygen content of the residue air will be lower than that of the feed air, because rubbery membranes are normally slightly more permeable to oxygen than to nitrogen.